1. Field of the Invention
The present invention generally relates to a coordinate indicating device and a coordinate measuring device for measuring input coordinates of the coordinate indicating device, and more particularly, to a coordinate indicating device which wirelessly receives drive power wirelessly transmitted by a coordinate measuring device.
2. Description of the Related Art
With the recent dramatic growth of the market associated with smart phones and touch screens, related research has also been actively conducted. To input a specific command in association with a smart phone or a touch screen, a user may input a specific command or designate a specific icon by placing a part of a user's body or a stylus pen in a specific position on a display.
As one of the input schemes of the stylus pen, an Electromagnetic Resonance (EMR) scheme is widely used. In the EMR scheme, a loop coil is disposed on a Printed Circuit Board (PCB), a voltage is applied to the loop coil to generate electromagnetic waves, and the generated electromagnetic waves are absorbed by an EMR pen. Herein, the EMR pen may include a condenser and a loop, and may emit the absorbed electromagnetic waves in a predetermined frequency.
The electromagnetic waves emitted from the EMR pen may be absorbed again into the loop coil of the PCB so that a position of a touch screen near the EMR pen may be determined based on the absorbed electromagnetic waves.
Power transmission based on electromagnetic induction transmits power between a primary coil and a secondary coil. Once a magnet moves in a coil, an induced current is generated and by using the induced current, a transmission side generates a magnetic field and a reception side induces a current according to a change of the magnetic field, thus producing energy. Such a phenomenon is called a magnetic induction phenomenon and a power transmission method using this phenomenon transmits energy very efficiently.
In regard to the resonance scheme, Soljacic, a professor at the Massachusetts Institute of Technology (MIT), announced in 2005 a system in which electricity is wirelessly transferred using a resonance-based power transmission principle, based on a coupled mode theory that operates even when a device to be charged is separated from a charging device by several meters. The wireless charging system used by the MIT team employed the concept in physics of resonance by which, when a tuning fork oscillates at a particular frequency, a wine glass next to the tuning fork will tend to oscillate at the same frequency. The research team resonated an electromagnetic wave containing electrical energy instead of resonating sounds. The resonated electrical energy is directly transferred only when there is a device having a resonance frequency, and parts of electrical energy that are not used are reabsorbed into an electromagnetic field instead of being spread in the air, so that the electrical energy does not affect surrounding machines or people, in contrast to other electromagnetic waves.
The electric field coupling method transmits and receives power through coupling between electric fields generated in terminals of the transmission side and the reception side. The electric field coupling method is advantageous in that the degree of freedom of a horizontal position and the height of the degree of freedom of electrode designing may be flexibly adjusted.
A recently developed stylus pen provides a frictional force or vibration to the user to allow the user to experience an environment similar to an actual writing environment of a writing tool. For example, the stylus pen provides a frictional force to the user so that the user may experience the same effect as when the user actually writes on paper using a pencil.
For the foregoing structure, the stylus pen may include a means for providing vibration or a frictional force, such as an actuator. Moreover, the stylus pen includes a battery for storing power necessary for the overall operation of the actuator and the overall operation of the stylus pen. Herein, the battery of the stylus pen may be rechargeable or non-rechargeable. If the battery is non-rechargeable, it needs to be replaced when the battery is discharged. For the rechargeable battery, an external power source for charging is required, causing inconvenience to the user.
Therefore, a need exists to develop a technique for providing power necessary for the stylus pen based on user convenience.